Cathode ray tube and image display apparatus using the same

ABSTRACT

An elastic support member  5  or an elastic support member-holding plate is located substantially in the middle portion of a frame portion ( 1  and  2 ), and a shadow mask is constructed such that a tension in the middle portion of the shadow mask  3  is larger than the tension in the edge portions of the shadow mask  3 . In another aspect, a plurality of elastic support members  5  are such that at least two elastic support members having substantially different spring constants are combined.

TECHNICAL FIELD

The present invention relates to a cathode ray tube (hereinbelow, calleda color picture tube in the specification) and an image displayapparatus using the same. More particularly, the invention relates to acolor picture tube which is characterized by an elastic support memberused to support a frame across which a mask is stretched in a statewhere a tensile force is applied thereto and to an image displayapparatus using the same.

BACKGROUND ART

A color picture tube has, as shown in FIG. 1, a structure including anenvelope constructed by a panel 52 and a funnel 53 joined to the panel52. In the periphery of the panel 52, a side wall 51 is formed. Aphosphor screen 54 having three colors of R, G, and B is formed on theinner face of the panel effective portion. A shadow mask 55 in which anumber of electron beam-passing apertures are formed is disposed so asto face the phosphor screen 54. The funnel 53 has a neck 56 in which anelectron gun 57 for emitting three electron beams is disposed. Bydeflecting the three electron beams by a magnetic field generated by adeflection yoke 80 attached on the outside of the funnel 53, and byhorizontally and vertically scanning the phosphor screen 54 via theshadow mask 55, a color image is displayed.

From the viewpoint of a smaller amount of entering external light andgood looking, the panel of a recent color picture tube is beingflattened and the shadow mask 55 is being accordingly flattened. Whenthe shadow mask 55 is flattened, the plane of the shadow mask 55 cannotbe maintained only by supporting the body of the shadow mask 55 by aframe 58. When the shadow mask 55 is simply supported only by the frame58, the shadow mask 55 easily vibrates by external vibration, so that anadverse influence is exerted on a display image of the color picturetube. Consequently, the shadow mask 55 is stretched across the frame 58in a state where a tensile force is applied thereto.

In a doming phenomenon that the surface of the shadow mask 55 isthermally deformed by collision of electron beams with the shadow mask55, when the shadow mask 55 is flattened, a displacement amount of theelectron beam becomes large especially around both the left and rightedge faces of the screen. In order to absorb the thermal expansioncaused by the collision of electron beams, a practically maximum tensionclose to the elastic limit is applied to the shadow mask 55.

In order to display an accurate color image on the phosphor screen 54 insuch a color picture tube, it is necessary to hold the shadow mask 55 ina predetermined alignment relationship to three-color phosphor layersconstructing the phosphor screen 54. One of the factors that deterioratethe alignment relationship between the shadow mask 55 and the phosphorscreen 54 is vibration of the shadow mask 55. Although a tensile forceis applied to the shadow mask 55 as described above, it is difficult tocompletely suppress the vibration of the shadow mask 55 only by thetensile force. The vibration of the shadow mask 55 occurs when externalvibration or impact (for example, the vibration of a loudspeakerdisposed on a side of the panel 52) is transmitted from the panel 52 viaan elastic support member 59 and the frame 58 to the shadow mask 55.When the shadow mask 55 vibrates, the distance between the shadow mask55 and the phosphor screen 54 changes, and thereby a landingdisplacement of the electron beam occurs. It is consequently desiredthat the vibration of the shadow mask 55 be attenuated as much aspossible in a short time.

In order to suppress the vibration of the shadow mask 55, it isnecessary to suppress the vibration of the shadow mask 55 itself and thevibration of the frame 58.

As a method of suppressing the vibration of the shadow mask 55 itself, acase where a damper is provided on an edge face of the shadow mask 55has been reported. FIG. 2 shows an example of the damper. This damper 61has a structure obtained by bending the ends of a wire. The damper 61 isprovided by passing the bent portions into openings 62 in the shadowmask 55. The size of the opening 62 in the shadow mask 55 is set so thatthe damper 61 can freely vibrate. When the shadow mask 55 vibrates, apart of the energy for vibrating the shadow mask 55 is used to vibratethe damper 61, so that the vibration of the shadow mask 55 isattenuated. Even the structure in which such dampers 61 are provided isinsufficient to demonstrate a vibration attenuating effect over theentire shadow mask 55.

On the other hand, in order to suppress the vibration of the frame 58,it is necessary to add a function such that the vibration can beabsorbed by converting the vibration energy of the frame 58 to, forexample, thermal energy (hereinbelow, called a damper function). As isdisclosed in Japanese Unexamined Patent Publication No. 9-293459, aconventional method in which a sliding portion is provided with theelastic support member 59 itself so as to suppress the vibration of theframe 58 by the generated friction has been reported. FIGS. 3A and 3Bshow the structure of the elastic support member disclosed in JapaneseUnexamined Patent Publication No. 9-293459. FIG. 3A is a front view andFIG. 3B is a side view. The structure has a matching portion 65 having amatching opening 64 to be matched to a stud pin 63, a fixed portion 66to be fixed to the frame 58, and connecting portions 67 for connectingthe matching portion 65 and the fixed portion 66. The connectingportions 67 are joined together by welding in their mid-portions so asto form a V shape. The fixed portion 66 has a blade 68 that is insertedinto an opening 69 formed in the matching portion 65. When the elasticsupport member expands and contracts in the directions indicated by thetwo-headed arrow as the frame vibrates, the blade 68 slides in theopening 69, thereby obtaining a damper function. However, such anelastic support member has a complicated structure and is not easilyproduced. Due to a problem of a high cost, it is difficult to actuallyadopt the elastic support member.

In addition, the shadow mask 55 has to be attached and detached aplurality of times during a process of forming the phosphor screen 54 bya photo printing method using the shadow mask 55 as a photo mask.Consequently, the elastic support member 59 for holding the frame 58across which the shadow mask 55 is stretched in a state where a tensileforce is applied thereto has to be easily attached and detached in thesame position with excellent reproducibility.

Further, in addition to the suppression of the vibration, the elasticsupport member 59 is required to have the following characteristics:

(1) improvements in terms of doming characteristic and low/hightemperature characteristic; and

(2) assurance of impact resistance.

Doming characteristic (phenomenon) of (1) is a phenomenon such that thetemperature of the shadow mask 55 rises due to the collision of electronbeams as described above, creating a temperature difference between theshadow mask 55 and the panel 52 (usually made of glass), and thereforethe predetermined alignment relationship deteriorates due to a thermalexpansion coefficient difference between the material of the shadow mask55 and that of the panel 52. Low/high temperature characteristic issimilar to doming characteristic and is a phenomenon such that apositional alignment relationship between the shadow mask 55 and thepanel is displaced due to the temperature difference between the shadowmask 55 and the panel 52 caused by the ambient temperature of the panel52. Both of the characteristics are phenomena that the positionalalignment relationship between the shadow mask 55 and the panel 52 isdisplaced due to the temperature difference between them. The phenomenacause a color shift and color unevenness. The displacements cannot becompletely compensated even if a tensile force is applied to the shadowmask 55. When the shadow mask 55 expands relatively, the displacementsbetween the shadow mask 55 and the inner face of the panel 52 on whichthe phosphor screen 54 is formed has to be compensated by shortening thedistance between the shadow mask 55 and the inner face of the panel 5.On the contrary, when the panel 52 expands, it is necessary to widen thedistance between the shadow mask 55 and the panel 52. In this manner,the elastic support member 59 has to have the function of displacing theposition of the shadow mask 55 in accordance with the temperaturedifference between the panel 52 and the shadow mask 55.

At the time of carrying the color picture tube, there is a case suchthat the color picture tube is subjected to an impact that cannot beimagined in a normal use state due to an unexpected event (such ascollapse of a cargo). When the shadow mask 55 is displaced due toplastic deformation of the elastic support member 59 or buckling of thematching portion by the impact, the positional alignment relationshipbetween the shadow mask 55 and the panel 52 is displaced. The elasticsupport member 59 therefore has to be strong enough not to cause adisplacement in the shadow mask 55 even when a specific impact(acceleration) is applied.

The structure including the frame, the shadow mask, and the elasticsupport member (hereinbelow, called a frame structure) is desired tohave overall excellent characteristics with respect to the suppressionof the vibration of the shadow mask, doming and low/high temperaturecharacteristics and impact resistance.

An example of the conventional frame structure will be describedhereinbelow. FIG. 4A is an entire view showing a state where a frame 58is disposed in the panel 62 with strip-shaped elastic support members59. FIG. 4B is an enlarged view of the strip-shaped elastic supportmember 59. The strip-shaped elastic support member 59 has a catchingportion 60(a) to be caught by a stud pin 63 of the panel 62, a fixedportion 60(b) to be fixed to the frame, and a connecting portion 60(c)for connecting the catching portion 60(a) and the fixed portion 60(b).Such a strip-shaped elastic support member is called a TCM type and hasa characteristic of excellent impact resistance. As a countermeasureagainst doming and low/high temperature characteristics, the elasticsupport member has a bimetallic structure made of two kinds of materialsa (hatched portion) and β (not-hatched portion) having different thermalexpansion coefficients. The bimetallic effect of the elastic supportmember 59 is not, however, displayed unless the temperature of theelastic support member 59 itself changes. Therefore, there is a problemof a slow response to a change in environment or a sudden rise intemperature of the shadow mask. Since the temperature change amount ofthe elastic support member 59 is small, a large correction amount cannotbe set. Consequently, there is another problem that a material of theshadow mask having a thermal expansion coefficient largely differentfrom that of the material of the panel cannot be used.

In the frame structure, since corners 74 of the frame 58 are notsupported, vibration easily occurs. Moreover, since the elastic supportmember of the TCM type has no damper effect, once vibration occurs, itis not attenuated easily. As a result, the shadow mask also vibrates,thereby causing a problem that an adverse influence such as a colorshift is exerted on the picture quality.

FIG. 5A shows a frame structure of another conventional technique. Asshown in FIG. 5, stud pins 71 are provided on the inner walls at theopposite corners of a panel 70. Each of elastic support members 72 has acatching portion 72(a) to be caught by the stud pin 71, a fixed portion72(b) fixed to a frame, and a V-shaped connecting portion 72(c) forconnecting the catching portion 72(a) and the fixed portion 72(b). Theconnecting portion 72(c) is attached to the phosphor screen side.However, the configuration has the following problems.

(1) The clearance between the panel 70 and the frame 73 is narrow sincethe elastic support members 72 are disposed at the opposite corners ofthe panel 70, so that the assembling is difficult. It is not easy toassemble the frame 73 to the panel 70, and reduction in yield due todamage in the elastic support member 72, the stud pin 71, and the panel70 is a problem.

(2) Since the elastic support members 72 are disposed at the oppositecorners of the panel 70, the elastic support member 72 cannot bewidened. Consequently, the impact resistance is poor.

DISCLOSURE OF THE INVENTION

The present invention is intended to solve the conventional problemsmentioned above and provide a color picture tube that is resistant toexternal vibration and is excellent in terms of doming and low/hightemperature characteristics and impact resistance, and has a suitableconfiguration for easy assembling, and an image display apparatus usingthe color picture tube.

The first aspect of the present invention is a cathode ray tubecomprising, at least, a panel having a phosphor screen formed thereon, ashadow mask having a plurality of electron beam-passing portions, and aframe across which the shadow mask is stretched in a state where atensile force is applied thereto, the frame being securely attached tothe panel by an elastic support member while the phosphor screen isopposed to the shadow mask, wherein the elastic support member islocated substantially in the middle portion of a frame portion and theshadow mask is configured such that the tension in the middle portion ofthe shadow mask is larger than the tension at the edge portions of theshadow mask.

In the configuration described above, since the elastic support memberis located substantially in the middle portion of the frame portion, theassembly and frame support may be improved, and since the tension in themiddle portion of the shadow mask is larger than the tension at the edgeportions of the shadow mask, the vibration attenuating effect of theelastic support member may be found not only at the edge portions of theshadow mask but also at the middle portion of the shadow mask.

The second aspect of the present invention is a cathode ray tubecomprising, at least, a panel having a phosphor screen formed thereon, ashadow mask having a plurality of electron beam-passing portions, and aframe across which the shadow mask is stretched in a state where atensile force is applied thereto, the frame being securely attached tothe panel by an elastic support member while the phosphor screen isopposed to the shadow mask, wherein the elastic support member is fixedto an elastic support member-holding plate located substantially in themiddle of the frame portion and the shadow mask is configured such thatthe tension in the middle portion of the shadow mask is larger than thetension at the edge portions of the shadow mask.

In the configuration described above, since the elastic support memberis fixed to the elastic support member-holding plate locatedsubstantially in the middle of each frame portion, the elastic supportmembers are located in the same plane by adjusting the extensiondirection of the elastic support member-holding plate even when theframe portions are not in the same plane, and therefore the effects ofthe first aspect of the present invention are demonstrated further.

In these first and second aspects of the present invention describedabove, the elastic support member desirably comprises a fixed portion tobe fixed to the frame, a matching portion to be matched to a stud pinprovided on the inside of the panel side wall, and a connecting portionfor connecting the matching portion and the fixed portion. Theconnecting portion preferably has an approximately V-shapedconfiguration. With this configuration, better doming and low/hightemperature characteristics may be obtained.

In this configuration, the fixed portion of the elastic support memberpreferably has an area of at least 5 cm². This is because when the areaof the fixed portion is made large, a force applied to the frame isdispersed, and this prevents the tension distribution pattern of theshadow mask from varying due to the frame deformation. To increase theeffect described above, the ratio of the area of the fixed portion ofthe elastic support member to the area of the frame portion to which theelastic support member is fixed is preferably at least greater than{fraction (1/25)}.

Furthermore, the elastic support member desirably includes a vibrationsuppressing structure, because the vibration of the frame is transmittedto the shadow mask even when the vibration of the shadow mask isattenuated unless the vibration of the frame is attenuated.

The spring constant of the elastic support member may be alteredrelatively easily without changing the size of the elastic supportmember by is forming an opening in the connecting portion of the elasticsupport member and adjusting the size of the opening.

The force applied to the frame portion by the elastic support member ispreferably in the range of 1 kgf to 8 kgf and the spring constant of theelastic support member is preferably in the range of 0.1 kgf/mm to 2.5kgf/mm.

The stretched shadow mask is provided with a damper for attenuating thevibration and has a tension distribution such that the tension islargest in the middle portion of the shadow mask and decreases graduallytoward the edge portions to ensure that the vibration may be attenuatedin the entire shadow mask. In order to extend the attenuating effect ofthe damper to the entire shadow mask, it is preferable that the tensiondistribution satisfy the relationships T1≧T2≧T3 and T1≧1.1×T3, where thetension of the shadow mask middle portion is T1, the tension of theshadow mask edge portions is T3, and the tension of the intermediateportions between the middle and the edge portions is T2.

Preferably, the damper has a structure that is freely movable with noportion thereof fixed to the shadow mask in order to improve theattenuating effect.

Specifically, the damper is preferably so constructed as to be insertedinto an opening formed in the shadow mask and is preferably a wire-likemember or a ring-like member.

As the material for the shadow mask, Fe—Ni alloy is preferable since itscreeping rate is small even when heated to higher temperatures.

The third aspect of the present invention is a cathode ray tubecomprising, at least, a panel having a phosphor screen formed thereon, amask having a plurality of electron beam-passing portions, and a frameon which the mask is held, the frame being securely attached to thepanel by a plurality of elastic support members while the phosphorscreen is opposed to the mask, wherein the plurality of elastic supportmembers are such that at least two elastic support members havingsubstantially different spring constants are combined.

In the composition described above, when the plurality of elasticsupport members are such that at least two elastic support membershaving substantially different spring constants are combined, singlevibration mode, in which the vibration is easily suppressed,predominates, and therefore the vibration of the frame may besuppressed.

In this third aspect of the present invention described above,desirably, each of the elastic support members is located substantiallyin the middle of a frame portion to suppress the vibration of the mask.

To obtain better doming and low/high temperature characteristics,desirably, the elastic support member comprises a fixed portion to befixed to the frame, a matching portion to be matched to a stud pinprovided on the inside of the panel side wall, and a connecting portionfor connecting the matching portion and the fixed portion. Theconnecting portion preferably has an approximately V-shapedconfiguration.

Of the elastic support members, opposing elastic support membersdesirably have the same spring constant in order to increase theintensity of single vibration further.

The fixed portion of the elastic support member preferably has an areaof at least 5 cm². This is because when the area of the fixed portion ismade large, the force applied to the frame is dispersed, and thisprevents the tension distribution pattern of the shadow mask fromvarying due to the frame deformation. To increase this effect describedabove, the ratio of the area of the fixed portion of the elastic supportmember to the area of the frame portion to which the elastic supportmember is fixed is preferably at least greater than {fraction (1/25)}.

The elastic support member desirably includes a vibration suppressingstructure, because the vibration of the frame is transmitted to theshadow mask even when the vibration of the shadow mask is attenuatedunless the vibration of the frame is attenuated.

The spring constant of the elastic support member may be alteredrelatively easily without changing the size of the elastic supportmember by forming an opening in the connecting portion of the elasticsupport member and adjusting the size of the opening.

The force applied to the frame portion by the elastic support member ispreferably in the range of 1 kgf to 8 kgf and the spring constant of theelastic support member is preferably in the range of 0.1 kgf/mm to 2.5kgf/mm.

Preferably, the mask is stretched across the frame in a state where atensile force is applied thereto, and more preferably, the tension inthe middle portion is larger than the tension at the edge portions inthe tension distribution of the mask. The reason for this is that thestretched shadow mask is provided with a damper for attenuating thevibration and has the tension distribution in which the tension islargest in the middle portion of the shadow mask and decreases graduallytoward the edge portions to ensure that the vibration may be attenuatedin the entire shadow mask. In order to extend the attenuating effect ofthe damper to the entire shadow mask, it is more preferable that thetension distribution satisfy the relationships T1≧T2≧T3 and T1≧1.1×T3,where the tension of the shadow mask middle portion is T1, the tensionof the shadow mask edge portion is T3, and the tension of theintermediate portions between the middle and the edge portions is T2.

Preferably, the damper has a structure which is freely movable with noportion thereof fixed to the shadow mask in order to increase theattenuating effect.

Specifically, the damper is preferably so constructed as to be insertedinto an opening formed in the shadow mask and is preferably a wire-likemember or a ring-like member.

As the material for the shadow mask, Fe—Ni alloy is preferable since itscreeping rate is small even when heated to higher temperatures.

Furthermore, the first, second, and third aspects of the presentinvention described above may be applied not only to the foregoingcathode ray tube but also to a general image display apparatus such as atelevision set which includes an electron beam controlling circuit, acabinet, and the like in addition to the cathode ray tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a color picture tube.

FIG. 2 is a perspective view showing a shadow mask in which a damper ofa conventional color picture tube is provided.

FIGS. 3A and B are views showing a conventional elastic support memberprovided with a damper function. FIG. 3A is a front view thereof andFIG. 3B is a side view thereof.

FIGS. 4A and B are views showing the structure of a conventional colorpicture tube, and FIG. 4A is a front view thereof and FIG. 4B is anenlarged perspective view thereof.

FIGS. 5A and B are views showing the structure of a conventional colorpicture tube. FIG. 5A is a front view thereof and FIG. 5B is an enlargedperspective view thereof.

FIG. 6 is a perspective view illustrating Embodiment 1.

FIG. 7 is a perspective view showing an elastic support member used inEmbodiment 1.

FIG. 8 is a phase diagram showing one example of a tension distributionof a shadow mask. FIG. 8A is a view showing an A-type distribution, andFIG. 8B is a view showing an M-type distribution.

FIG. 9 is a phase diagram showing changes in the tension distribution ofa shadow mask.

FIG. 10 is a perspective view showing one form of the dampers.

FIG. 11 is a perspective view showing another form of the dampers.

FIG. 12 is a graph showing the relationship between T1/T3 and vibrationsuppressing time.

FIG. 13 is a view showing a variation of the elastic support member.

FIG. 13A is a perspective view thereof, and FIG. 13B is a crosssectional view thereof.

FIG. 14 is a view showing another variation of the elastic supportmember. FIG. 14A is a perspective view thereof, and FIG. 14B is a crosssectional view thereof.

FIG. 15 is a perspective view showing an elastic support member used inEmbodiment 2.

FIG. 16 is a perspective view showing an elastic support member used inEmbodiment 3.

FIG. 17 is a phase diagram showing the condition of the attenuatedvibration of a frame in Embodiment 3.

FIG. 18 is phase diagram showing the result of analysis of the vibrationmodes of a frame.

FIG. 19 is a perspective view showing the movement of an elastic supportmember at the time of torsional vibration mode.

FIG. 20 is a cross sectional view showing the movement of an elasticsupport member at the time of single vibration mode.

FIG. 21 is a perspective view showing Embodiment 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be explained in detailswith reference to the drawings. The shadow mask of the color picturetube explained hereinbelow is a flat-faced mask, and the constructioinof the color picture tube having been explained with reference to FIG. 1also applies to the following embodiments.

EMBODIMENT 1

FIG. 6 is a perspective view of frame portions according to Embodiment 1of the present invention. In FIG. 6, reference numeral 1 denotes leftand right frame portions, and reference numeral 2 upper and lower frameportions wherein a shadow mask 3 is stretched in a state where a tensileforce is applied in vertical directions (as indicated by the two-headedarrow). Wire-like dampers 4 for attenuating the vibration of the shadowmask are provided on left and right edge surface portions of the shadowmask 3. In the embodiment, a 29-inch frame is used and the shadow mask 3has a tension distribution set to 4.3 kgf/mm² for the middle portion,3.4 kgf/mm² for the left and right edge surface portions, and 3.6kgf/mm² for intermediate portions between the middle portion and theleft and right edge surface portions. 36% Ni—Fe alloy was employed formanufacturing the shadow mask 3.

Elastic support members 5 for attaching the frame to the panel arelocated substantially in the middle portions of the frame portions 1,2in view of assembly and support of the frame portions 1, 2 {on-axial SP(spring) structure}. FIG. 7 illustrates an enlarged view of the elasticsupport member 5 employed in the embodiment. The elastic support member5 comprises a fixed portion 6 to be fixed to the frame portion, amatching portion 7 to be matched to a stud pin provided on the inside ofthe panel side wall, and a V-shaped connecting portion 8 for connectingthe fixed portion 6 and the matching portion 7, the connecting portion 8having an opening 13. It is possible to determine a spring constant forthe elastic support member 5 by varying the size of the opening 13(particularly its length L) and the plate thickness of the connectingportion 8, wherein L is set to be 25 mm, the plate thickness 0.6 mm andthe spring constant 1.2 kgf/mm in the embodiment.

For demonstrating the vibration attenuating effect over the entireshadow mask 3, it is desirable that the tension distribution be suchthat the tension in the middle portion of the shadow mask is largestwhile it becomes gradually lower toward the edge portions (hereinafterreferred to as “A-type distribution”) as illustrated in FIG. 8A. This isbecause in a distribution such that a tension peak is obtained somewhereother than the middle portion (hereinafter referred to as “M-typedistribution”) as is shown in FIG. 8B, the vibration attenuating effectowing to dampers do not cover the region (b) of the middle portion whilethe vibration attenuating effect are recognized on the regions (a)extending from the edge portions up to where the peak tension isobtained. This is due to the fact that spot P where the peak tension isachieved vibrates as being a node so that the extension of the vibrationattenuating effect of the dampers are suppressed at the tension peak. Itshould be noted that the vibration attenuating effect is prevented fromexpanding due to similar reasons even when the shadow mask includeswrinkles or irregularities in tension.

Experiments

The above-described shadow mask frame was assembled into a CRT andevaluated. The results are indicated in Table 1. It should be noted thatthis Table 1 also includes the results obtained by using stripplate-like elastic support members of the prior art (hereinafterreferred to as “TCM type”) and those illustrated in Embodiment 2.

TABLE 1 Results on Characteristics Evaluation (29-inch) Prior ArtEmbodiment 1 Embodiment 2 (TCM type) Assess- Assess- Assess- ItemTargets Results ment Results ment Result ment Vibration Color shift 1.5sec Good 1.6 sec Good 1 sec Good tapping test continuity *1 2 sec orless Loudspeaker No color shift No color Good No color Good No colorGood test *2 shift shift shift Low/high 1 μm/° C. or 0.9 Good 1 μm/° C.Good 1.5 μm/° C. Poor temperature lower μm/° C. Characteristic Overall30 μm or less 20-30 Good 28 μm Good 40 μm Poor doming μm Drop (impact-Displacement 15-20 Good 20 μm Good 100 μm or Poor resistance) amount ofμm greater test frame (35 G: 40 ms) position 20 μm or less

As it is evident from Table 1, the targets in all items were attained,and the frame proved to be strong against external vibration and to besuperior in terms of doming and low/high temperature characteristics aswell as impact resistance. The frame may also be easily assembled sinceit is of on-axial SP structure, and a fraction defective during theprocess of attaching the frame to the panel (including photolithographprocess) was remarkably decreased to be not more than {fraction (1/10)}.

The conventional TCM type elastic support member was not sufficient interms of doming characteristic, low/high temperature characteristic, andimpact resistance. Therefore, an elastic support member having theabove-mentioned construction (hereinafter referred to as “mechanicaltype”) is desirable.

Supplementary Remarks

(1) While the area of the fixed portion 6 of the elastic support member5 in which is fixed to the frame as employed in Embodiment 1 was set tobe 10 cm², but the present invention is not limited to this value. Itshould, however, be noted that this area be desirably as large aspossible, and preferably 5 cm² at the minimum. This is because a smallarea of the fixed portions 6 may result in deformation of the framesince the force applied on the frame by the elastic support member 5focuses thereon and thereby changes the pattern of the tensiondistribution of the shadow mask 3 as illustrated in FIG. 9. As has beenexplained, changes in the tension distribution pattern are notpreferable since they create regions in which the vibration of theshadow mask is hard to be attenuated. For these reasons, the area of thefixed portion 6 of the elastic support member 5 in which is fixed to theframe is desirably as large as possible, and preferably 5 cm² at theminimum.

(2) While it is possible to prevent the vibration of the shadow mask 3by setting the area of the fixed portion 6 of the elastic support member5 in which is fixed to the frame to be larger than 5 cm², as describedabove, in Embodiment 1 (wherein the panel size is of 29-inch), thismethod is also applicable to panels of different sizes. It has beenconfirmed through experiments that similar effects may be obtained bysetting a ratio (A1/A2) of the area (A1 cm²) of the fixed portion 6 ofthe elastic support member 5 to the area (A2 cm²) of the frame portionto which the elastic support member 5 is fixed to be larger than{fraction (1/25)}.

(3) Although employed in Embodiment 1 is a mechanical type elasticsupport member 5 having a spring constant of 1.2 kgf/mm and the forceapplied to the frame portion when the frame is disposed in the panel isapproximately 3.5 kgf, the mechanical type elastic support member 5 thatmay be applied to the present invention is not limited to this. However,the force applied to the frame portion is preferably in the range of 1kgf to 8 kgf. This is because the disposing condition of the frame tothe mask is unstable when the force is less than 1 kgf while the frameis deformed when the force exceeds 8 kgf, and the tension distributionof the shadow mask 3 changes into M-type whereby the vibration becomeshard to be attenuated.

It has thus been confirmed through experiments that it is preferable toset the spring constant of the mechanical type elastic support member 5to be in the range of 0.1 kgf/mm to 2.5 kgf/mm for realizing theabove-described disposing condition. Because a realizable maximum limitof the clearance between the frame and the panel is 20 mm (and smallerwhen the panel size is smaller), the spring constant needs to be notless than 0.1 kgf/mm for realizing the above-mentioned force fordisposing. On the other hand, when the spring constant exceeds 2.5kgf/mm, the spring constant rigidity becomes large enough not to causethe deformation, thereby remarkably worsening the assemblingcharacteristics, and even when the same amount of force is applied, thedeformation occurs only in a small amount. As a result, good domingcharacteristic and low/high temperature characteristic remarkablydeteriorate.

(4) While each damper 4 provided on the left and right edge surfaceportions of the shadow mask 3 is constructed such that a wire-likemember is partially bent to be inserted into the opening 21 formed inthe shadow mask 3 in Embodiment 1, the damper 4 applicable to thepresent invention is not limited to this type, and it may also be aring-like member 9 illustrated in FIG. 10. It may alternatively be adamper 11 such that one portion thereof contacts an edge surface 12 ofthe shadow mask while another portion is fixedly attached to a frame 10as illustrated in FIG. 11.

(5) The material for the shadow mask desirably has a small thermalcreeping rate in a high temperature condition in a state where a tensionis applied thereto. In a CRT manufacturing process, it is necessary toperform a plurality of high temperature heat treatment processes such asa heat process for easing the stress generated at the time of stretchingthe shadow mask, a fritting process of forming an exterior tube, and thelike. In a construction in which the shadow mask with a tension appliedis stretched across the frame, it is not preferable that the thermalcreeping take place in the shadow mask during the heat treatmentprocesses because phenomena such as a decrease in tension, a change inthe tension distribution, wrinkles in the shadow mask, and the likeoccur. In order to absorb the thermal creeping, it is required to applyquite a large tension to the shadow mask. This involves an increase inthe frame strength, thereby leading to other problems such as anincrease in frame weight, more complicated and expensive stretchingequipment, complications in the process, and the like. Thus, it isdesirable to select, as the material for the shadow mask, a materialsuch as Ni—Fe alloy (Invar material) as employed in Embodiment 1 or thelike that exhibits a small thermal creeping rate in a high temperaturecondition in a state where a tension is applied thereto.

(6) For expanding the vibration attenuating effect of the dampers overthe entire shadow mask, it is preferable to set the tension distributionof the shadow mask so as to satisfy the relationships T1≧T2≧T3 andT1≧1.1×T3, where T1 is a tension at the middle portion of the shadowmask, T3 a tension at the edge portions, and T2 a tension of theintermediate portions between the middle portion and the edge portions.This is due to the fact that the vibration suppressing time becomeslonger when the relationship T1<1.1×T3 is satisfied as illustrated inFIG. 12. Note that the vibration suppressing time means a time requiredfor attenuating amplitude of vibration to {fraction (1/10)} or lower.

(7) It is desirable that the elastic support member comprises avibration suppressing structure that is achieved through means such aswelding a sliding member 33 having a cylindrical cross-sectional shapeto the fixed portion so as to slide to a tip end of the stud pin 34 asillustrated in FIGS. 13A and B, welding a strip-like sliding member 35to the fixed portion 6 so as to slide to the tip end of the stud pin 34as illustrated in FIG. 14, or the like. This is due to the fact that thevibration is transmitted to the shadow mask even when the vibration ofthe frame is attenuated unless the vibration of frame is attenuated.

EMBODIMENT 2

FIG. 15 is a perspective view of frame portions according to Embodiment2 of the present invention. It should be noted that members havingfunctions identical to those of Embodiment 1 are denoted by the samereference numerals, and therefore the explanations are omitted.

Embodiment 2 is of similar construction as that of Embodiment 1 expectthat among the elastic support members 5 for attaching the frame to thepanel, those disposed corresponding to the upper and lower frameportions 2 are fixed to elastic support member-holding plates 20 locatedsubstantially in the middle portions of the upper and lower frameportions 2 (the area of each elastic support member-holding plate 20fixed to the upper and lower frame portions 2 is 15 cm²), and that theshadow mask 3 has a tension distribution set to 4.0 kgf/mm² for themiddle portion, 3.2 kgf/mm² for the left and right edge surfaceportions, and 3.5 kgf/mm² for the intermediate portions between themiddle portion and the left and right edge surface portions.

Experiments

The above-described shadow mask frame was assembled into a CRT andevaluated. The results are indicated in the above Table 1. Similarly toEmbodiment 1, the targets in all items were attained and the frameproved to be strong against external vibration and to be superior interms of doming and low/high temperature characteristics as well asimpact resistance. The frame may also be easily assembled since it is ofon-axial SP structure, and a fraction defective during the process ofattaching the frame to the panel (including photolithograph process) wasremarkably decreased to be not more than {fraction (1/10)}.

Supplementary Remarks

(1) to (7) of Embodiment 1 also applies to Embodiment 2, and thereforethe explanations are omitted.

EMBODIMENT 3

FIG. 16 is a perspective view of an elastic support member according toEmbodiment 3 of the present invention. It should be noted that membershaving functions identical to those of Embodiment 1 are denoted by thesame reference numerals, and therefore the explanations are omitted.

Embodiment 3 is of similar construction as that of Embodiment 1 expectthat the elastic support members disposed to the upper and lower frameportions 2 have spring constants of 0.2 kgf/mm (L1: 50 mm, L2: 25 mm,t:0.3 mm) and that the elastic support members disposed to the left andright frame portions 1 have spring constants of 1.2 kgf/mm (L1: 50 mm,L2: 25 mm, t:0.6 mm). Note that the forces applied to the frame portionswere 1.2 kgf and 3.5 kgf, respectively, when the frame was disposed inthe panel by using these elastic support members.

Experiments

A frame structure as the one described above was assembled into a CRTand evaluated. The results are indicated in Table 2.

TABLE 2 Results on Characteristics Evaluation (29-inch) Embodiment 3PriorArt Results As- TCM type Results sess- Results Assess- Item Targetment ment Vibration Color shift 0.5 sec Good 1.5 sec Good tapping 2 sectest *1 or less Loud- No color No No Good speaker shift color color test*2 shift shift Low/high  1 μm/ 0.9 μm/ Good 1.5 μm/ Poor tempera- ° C. °C. ° C. ture or lower character- istic Overall 30 μm 20-30 μm Good 40 μmPoor doming or less Drop Displace- 15-20 μm Good 100 μm Poor (impactment or greater resistance) amount test of frame (35 G:40 position ms)20 μm or less

As it is evident from Table 2, the targets in all items were attained,and the frame proved to be strong against external vibration and to besuperior in terms of doming and low/high temperature characteristics aswell as impact resistance. Particularly in view of vibration, thevibration of the frame was suppressed in a time of 0.5 seconds or lesseven when such an impact as to have an acceleration of 3G was applied tothe panel as illustrated in FIG. 17B. The frame may also be easilyassembled since it is of on-axial SP structure, and a fraction defectiveduring the process of attaching the frame to the panel (includingphotolithograph process) was remarkably decreased to be not more than{fraction (1/10)}.

On the other hand, the conventional TCM type frame was not sufficient interms of doming characteristic, low/high temperature characteristic andimpact resistance. Therefore, the above mechanical type is desirable.

In this manner, the elastic support member of Embodiment 3 is effectivein suppressing the vibration of the frame, and the principle will now beexplained. In analyzing the vibration modes of the frame structure inwhich the mechanical type elastic support members are locatedsubstantially in the middle portions of the frame portions, it was foundthat three modes existed as illustrated in FIG. 18 (the results ofanalysis illustrated in FIG. 18 are those of a 29-inch panel. When thesize of the panel is varied, the generated frequency of the modeschanges though the mode shapes are the same).

(1) Torsional vibration mode: a mode in which the frame vibrates so asto have torsion (occurring in the proximity of 85 Hz in the case of a29-inch frame).

(2) Single vibration mode: a mode in which the frame rotationallyvibrates on the axis between the elastic support members fixed to theupper and lower frame portions or the elastic support members fixed tothe left and right frame portions (occurring in the proximity of 115 Hzand 130 Hz in the case of a 29-inch frame).

(3) Parallel vibration mode: a vibration mode in which the frameperforms parallel movements in a direction of the tube axis (thedirection as indicated by arrow A in the drawing) (occurring in theproximity of 140 Hz in the case of a 29-inch frame).

The conditions of the attenuated vibration were measured as follows(referred to as “loudspeaker single tone test”): a loudspeaker was setonto the panel surface, a vibration having a frequency only enough togenerate the respective vibration modes was applied thereto, and thenthe loudspeaker was turned off. It was found that the vibration could behardly attenuated in the torsional vibration mode and the vibrationcontinued. In the single vibration mode, the vibration could beattenuated in a time of not more than {fraction (1/10)} of that requiredfor the torsional vibration mode. In the parallel vibration mode, thevibration was attenuated as quick as measuring was nearly impossible.

The reasons for this may be attributed to the movements of the elasticsupport members. In the case of the torsional vibration mode, each ofthe elastic support members so shook about the stud pins 85 as to causetorsion to a matching portion 86(a) or a connecting portion 86(c) of theelastic support member as illustrated in FIG. 19. In such movements,because the elastic support member has no damper effect, the vibrationof the frame continues without being suppressed. In the single vibrationmode, the elastic support members, serving as a fulcrum, show the samemovements as those of the torsional mode while the other elastic supportmembers perform expanding and contracting movements as illustrated inFIG. 20 (expanding and contacting movements are performed in thedirections indicated by the two-headed arrow). At this time, a matchingopening 87 and the stud pin 85 of the elastic support member slideslightly with respect to the stud pin 85 and the matching portion 86(a)of the elastic support member. The friction caused by the sliding of thematching opening 87 and the stud pin 85 becomes a damper function,thereby serving to suppress the vibration of the frame. In the parallelvibration mode, all the elastic support members perform the expandingand contracting movements, thereby creating quite a large damperfunction so that the vibration of the frame is instantly suppressed.

All the elastic support members disposed to the left and right frameportions and the upper and lower frame portions are identical (in shape,in spring constant, and the like) in most cases. If this is the case,the vibration of the frame is mainly of the torsional mode and thesingle vibration mode or the parallel vibration mode hardly occurs.Thus, the vibration of the frame continues without being suppressed. Itwas found that the two vibration modes of the single vibration mode andthe parallel vibration mode could be brought about by employing elasticsupport members having different spring constants.

Table 3 illustrates the results of the intensity ratios of the torsionalmode and the single vibration mode were obtained in the case that thespring constants of the elastic support members disposed to the upperand lower frame portions were fixed to be 0.2 kgf/mm, and the springconstants of the elastic support members disposed to the left and rightframe portions were varied in the range of 0.2 kgf/mm to 1.9 kgf/mm.

TABLE 3 Spring constant of the springs disposed to the upper and lowerframe portions: 0.2 kgf/mm Spring constant of the Vibration intensitysprings disposed to the (relative ratio) left and right Torsional Singleframe portions mode vibration mode k: 0.2 kgf/mm 5 0 k: 1.2 kgf/mm 3 1.7k: 1.5 kgf/mm 1 0.5 k: 1.9 kgf/mm 0.6 0.7

The intensities as illustrated in Table 3 are the relative values in acase where the vibration intensity of a measuring system when externalvibration is applied is set to be 1. It can be understood from theseresults that the single vibration mode predominates by varying thespring constants of the elastic support members for the left and rightframe portions and for the upper and lower frame portions.

By varying the spring constants of the elastic support members in theabove manner, a part of the torsional vibration mode can be switched tothe single vibration mode so that the vibration of the frame can besuppressed. An effective means to increase the intensity of the singlevibration mode is that the opposing elastic support members disposed tothe upper and lower frame portions have the same spring constant and theopposing elastic support members disposed to the left and right frameportions have the same spring constant.

The spring constant of each elastic support member can be relativelyeasily varied without varying the size of the elastic support member byforming an opening in the connecting portion of the elastic supportmember and adjusting the size of the opening.

Supplementary Remarks

(1) to (7) of Embodiment 1 also applies to Embodiment 3, and thereforethe explanations are omitted.

(8) In Embodiment 3, the elastic support members are directly disposedto the frame. However, the invention is not limited thereto. As shown inEmbodiment 2, the elastic support member may be disposed to the framewith the elastic support member-holding plate interposed therebetween.

(9) According to Embodiment 3 of the present invention, each of theelastic support members is located substantially in the middle of aframe portion. While the invention is not limited thereto, it should benoted that it is preferable that the elastic support member is locatedsubstantially in the middle of the frame portion in order to suppressthe vibration of the mask, more effectively.

(10) In order to increase the intensity of the single vibration mode, itis desired that of the elastic support members, opposing elastic supportmember have the same spring constant.

(11) It is preferable that the mask is stretched across the frame in astate where a tensile force (tension) is applied thereto. In this case,it is more preferable that the tension distribution of the mask be suchthat the tension in the middle is larger than the tension at the edgeportions. This is because in the shadow mask in which a damper forattenuating the vibration is provided, the vibration of the entire maskcan be certainly attenuated by providing a tension distribution in whichthe tension is largest in the middle portion while it becomes graduallylower toward the edge portions.

(12) The third aspect of the present invention can be applied to a maskin which a flat-faced mask provided with a plurality of electronbeam-passing apertures are stretched in the vertical/horizontaldirection, and also a mask in which a plurality of thin lines calledaperture grills are stretched in the vertical direction. Incidentally,furthermore, the shadow mask is not limited to the flat-faced mask, andmay be a mask being stretched so as to have a cylindrical surface.

EMBODIMENT 4

Embodiment 4 of the present invention is a TV set to which the colorpicture tube according to Embodiments 1 to 3 is applied. FIG. 21 is aperspective view showing an outline of Embodiment 4. Reference numeral25 denotes a color picture tube of the present invention. Referencenumeral 26 denotes a loudspeaker. Reference numeral 27 denotes a circuitsuch as an electron beam controlling and tuner. With such structure, aflat TV set in which color shift caused by external vibration is smalland reliability against unexpected accidents at the time oftransportation is high is realized.

Incidentally, the structure of the present invention is not limited tothe TV set, and may be applied to a general image display apparatusessuch as a monitor.

INDUSTRIAL APPLICABILITY

As has been described above, the present invention is advantageous inthat it provides a color picture tube that has a strong resistance toexternal vibration, good doming and low/high temperaturecharacteristics, and good impact resistance and is easy to be assembled.The invention also provides a flat TV set employing the color picturetube.

What is claimed is:
 1. A cathode ray tube, comprising at least a panelhaving a phosphor screen thereon, a shadow mask having a plurality ofelectron beam-passing portions, and a frame across which the shadow maskis stretched so that a tensile force is applied thereto, the frame beingsecurely attached to the panel by an elastic support member and thephosphor screen is opposed to the shadow mask, wherein: the elasticsupport member is located substantially in the middle portion of theframe; the spring constant of the elastic support member is in the rangeof 0.1 kgf/mm to 2.5 kgf/mm when the frame is located in the panel withthe elastic support member; and the shadow mask is configured such thatthe tension in a middle portion of the shadow mask is larger than thetension at edge portions of the shadow mask.
 2. A cathode ray tube,comprising at least a panel having a phosphor screen thereon and a panelside wall, a shadow mask having a plurality of electron beam-passingportions, and a frame across which the shadow mask is stretched so thata tensile force is applied thereto, the frame being securely attached tothe panel by an elastic support member and the phosphor screen isopposed to the shadow mask, wherein: the elastic support member islocated substantially in a middle portion of the frame; the elasticsupport member comprises a fixed portion fixed to the frame, a matchingportion matched to a stud pin located on the inside of the panel sidewall, and a connecting portion connecting the matching portion and thefixed portion; the spring constant of the elastic support member is inthe range of 0.1 kgf/mm to 2.5 kgf/mm; and the shadow mask is configuredsuch that the tension in a middle portion of the shadow mask is largerthan the tension at the edge portions of the shadow mask.
 3. The cathoderay tube according to claim 2, wherein the connecting portion has anapproximately V-shaped configuration.
 4. The cathode ray tube accordingto claim 2, wherein the fixed portion of the elastic support member hasan area of at least 5 cm².
 5. The cathode ray tube according to claim 2,wherein the ratio of the area of the fixed portion of the elasticsupport member to the area of the frame portion to which the elasticsupport member is greater than {fraction (1/25)}.
 6. The cathode raytube according to claim 2, wherein the elastic support member includes avibration suppressing structure.
 7. The cathode ray tube according toclaim 2, wherein the connecting portion of the elastic support memberhas an opening having a predetermined size that determines the springconstant of the elastic support member.
 8. The cathode ray tubeaccording to claim 2, wherein the shadow mask comprises a damper forattenuating vibration.
 9. The cathode ray tube according to claim 8,wherein the damper is freely movable relative to the shadow mask. 10.The cathode ray tube according to claim 9, wherein the damper is locatedin an opening in the shadow mask.
 11. The cathode ray tube according toclaim 10, wherein the damper is a wire-like member.
 12. The cathode raytube according to claim 10, wherein the damper is a ring-like member.13. The cathode ray tube according to claim 2, wherein the shadow maskcomprises a Fe—Ni alloy.
 14. The cathode ray tube according to claim 2,wherein the elastic support member is fixed to an elastic supportmember-holding plate located substantially in the middle of the frame.15. The cathode ray tube according to claim 14, wherein the elasticsupport member includes a vibration suppressing structure.
 16. Thecathode ray tube according to claim 14, wherein the shadow maskcomprises a damper for attenuating vibration.
 17. The cathode ray tubeaccording to claim 16, wherein the damper is freely movable relative tothe shadow mask.
 18. The cathode ray tube according to claim 17, whereinthe damper is located in an opening in the shadow mask.
 19. The cathoderay tube according to claim 18, wherein the damper is a wire-likemember.
 20. The cathode ray tube according to claim 18, wherein thedamper is a ring-like member.
 21. The cathode ray tube according toclaim 14, wherein the shadow mask comprises a Fe—Ni alloy.
 22. An imagedisplay apparatus, comprising: a cathode ray tube, an electron beamcontrolling circuit and a cabinet, wherein the cathode ray; tubecomprises: at least a panel having a phosphor screen thereon, a shadowmask having a plurality of electron beam-passing portions, and a frameacross which the shadow mask is stretched so that a tensile force isapplied thereto, the frame being securely attached to the panel by anelastic support member and the phosphor screen is opposed to the shadowmask, wherein: the elastic support member is located substantially inthe middle portion of the frame; the spring constant of the elasticsupport member is in the range of 0.1 kgf/mm to 2.5 kgf/mm when theframe is located in the panel with the elastic support member; and theshadow mask is configured such that the tension in a middle portion ofthe shadow mask is larger than the tension at edge portions of theshadow mask.
 23. The image display apparatus according to claim 22,further comprising a loudspeaker connected to the display apparatus.